This invention relates to hydraulic systems and, more specifically, to flow control in hydraulic systems.
Many hydraulic systems in use today utilize pumps that are pressure compensated and/or flow and pressure compensated. When the outputs of such pumps are directed to hydraulic motors such as double-acting hydraulic cylinders, some means must be provided to match the flow of fluid from the pump to the motor with the flow of fluid from the motor to the system reservoir. Such flow matching not only prevents cavitation in so-called negative load conditions, but also prevents the increasing of pump output pressure which would occur due to the operation of its pressure compensation circuit if the flows were not matched.
Flow matching, while attainable, is an expensive feature in a hydraulic system in that it requires the provision of controlled size orifices or matched springs in flow control valves when achieved according to many prior art teachings.
When achieved according to other prior art teachings, it has been accomplished solely by monitoring the exhaust flow from the hydraulic motor and, as a practical matter, this has resulted in rather unwieldy valve designs requiring many cores for the various passages and cross connections of certain of the cores. This, in turn, has required the use of bridging elements which may be subject to leakage, thereby decreasing system efficiency and/or the location of fluid ports in a large variety of planes within the valve body, all of which add considerable expense to the cost of the valve.